Two-stroke internal combustion engine



Nov. 5, 1940. H. R. RICARDO TWO-STROKE INTERNAL COMBUSTION ENGINE Filed Nov. 3, 1959 5 Sheets-Sheet 1 Inventor m NOV. 5, 1940. RlCARDQ 2,220,662

TWO-STROKE INTERNAL COMBUSTION ENGINE Filed Nov. 3, 1939 5 Sheets-Sheet 2 v1 cu" '7 1 .2 v g LL,

WM wALM N 1940- H. R. RICARDO TWO-STROKE INTERNAL COMBUSTION ENGINE Filed Nov. vs, 1959 5 Sheets-Sheet 3' A TTOP/VEKS Patented Nov. 5, 1940 UNITED STATES PATENT OFFICE Harry Ralph Ricardo, London, England Application November3, 1930, Serial No. 3021760 In Great Britain November 2, 1938 2 Claims.

from a scavengingptir belt to which air is de-- livered by a displacer pump. This pump comprises a cylinder with a piston therein which is reciprocated by a link whichconnects it to .the

engine crankshaft so that the pump is driven at crankshaft speed.

An object of the present invention is to provide a construction of the above-mentioned displacer pump and the means of operating it so that a certain desired phasing relation,--as described here-' under, may be obtained between the working piston and the pump piston and a. compact design of engine can be obtained together with other advantagesindicated hereunder. A further object is to combinewith such an'arran-gement means whereby any baokflow or tendency to backflow of exhaust gases from the working cylinder into the scavenging belt, when the ports in'the wall of the cylinder begin to be uncovered, may be prevented or materially reduced.

According to this invention the piston of the pump is guided and supported by and reciprocates would otherwise tendto occur, being thus o'bviated or lesseried. With this construction of displacerpump there is combined a mechanically operated valve, preferably of. the rotary :type, which is arranged and operates to cut oil the pump and closethe .transfer'passage through which air is delivered by the pump to the scavenging beltapproinmately at the end of the delivery stroke of the pump piston whereby a'charge of air under a pressure, substantially above the mean pressure existent throughout the scavenging period, is trapped in the scavenging belt and that part of the transfer passage. which lies between the valve and the scavenging belt. The displacer pump whilebeing driven "at crankshaft speed is so out of phase with the 'work in'g' piston that the pump piston'beginsits delivery stroke at or about and preferably shortly before} the commencement of the scavenging period and ends This rod this stroke after the scavenging ports have been closed by the working piston. Conveniently the valve not only controls the commencement and termination of the delivery of air from the pump into the transfer passage, but also controls the commencement and termination of the inflow of air to the pump cylinder during the suction stroke of the piston therein.

The pump cylinder isdisposed with its axis approximately at right angles to theaxis of the working cylinder and the crankshaft axis. Owing to the construction above indicated and in particular the means for guiding the pumppis- Man, it is possible to position the displacer pump so that its axis lies in a horizontal plane at one 15 side of the crankcase in amanner which con,-

tributes to a compact design of that part of the engine. The valve,.if'of the rot ry type as is preferred, may be arrangedabove .t I e displacer pump with the transfer passage running past the-valve from the pump cylinder to the scavenging belt. I

The accompanying drawings illustrate by way of-an example an engine construction provided with a displacer pump embodying the present invention. .In .the drawings, Figure 1 is a vertical 25 sectional view of the improved engine showing the working cylinder, cranks ft and pump-cylinder, the section being taken normal to the crankshaft axis and through the axis of the pump cylinder. .Figure .2 is a longitudinal section 30 through the rotary valve controlling the pump suction and delivery,the section'being taken on the line 22 in Figure 3 looking in the direction of the arrows, and ,Figure 3 is a sectional end elevation showing the manner in which the rotary 35- 'valve and certain auxiliaries are driven from the crankshaft. These drawings show the invention as applied to an engine operating with compression ignition, but it is to be pnderstood that the ,useof :theinvention is notconfined to engines of Ithattype.

The two-stroke engine here shown has the following principal features. In the head A of the cylinder B is. acombustion chamberC of the openf type into which at the end of the compres'si'on stroke there is forced by the piston as much of the air charge as is practicable from the constructional 'point'of view. In this combustion chamber is an exhaust port, controlled by a poppet valve D. As will be seen the combustion chama 50,-

the combustion chamber. The inlet ports-h are 55.

formed in the wall of the cylnder B, the latter being conveniently constituted by a liner inserted a as shown in an outer water jacket casing B. The cylinder may, however, be formed otherwise. The inlet ports are formed as passages E through what is preferably a thickened part B of the wall of the cylinder or liner B, these passages leading inder H to the cavenging belt F is formed in the.

wall or outer part of the crankcase G However this transfer passage may be formed separately and arranged so as to lead to the scavenging belt F over the exterior of the crankcase.

The displacement pump comprises a cylinder H with a piston J therein. This cylinder is preferably formed integral with the crankcase G though it may be separate and mounted on the crankcase. The cylinder l-I projects from the crankcase with its axis at'right angles with respect to both the axis of the crankshaft K and the axis of the working cylinder B. 'The axis of the pump cylinder H lies in. a horizontal plane situated somewhat below the horizontal plane in which lies the axis of the crankshaft K.

Extending right through the displacer cylinder H from the outer end cover H to the spider plate H, which lies over the inner end of the cylinder H, is a guide rod L This may conveniently be formed hollow and fixed in place in the manner shown by the bolt L which extends not only through the spider plate H but also through the cylinder cover H The piston J slides on and is supported by this guide rod L which passesright through the piston. Thus this rod not only carries the weight of the piston, but also sustains the angular thrust of a link M which extends from the piston J to some conveniently placed pivot pin M on the big end of the cohnecting rod N of the working piston 0. 7

This arrangement has several advantages. It reduces the frictional loss arising from the reciprocation of the pump piston J and obviates wear of the cylinder H which would otherwise take place, and it enables the displacerpump to be designed and situated at the side of the crankcase so as'to contribute to compactness in the design of the whole engine. Weight and space can also be saved in that the piston J need not be so that the line of action of the centre of gravity of the reciprocating parts of the displacer pump lies approximately at right angles to the line of action of the'centre of gravity of the reciprocating parts associated with the main piston O, and by also arranging that the phase relation between the pump piston J and the working piston is approximately 90", a good balance may be achieved.

This arrangement of parts, however, in the absence of a suitabletiming valve, would make it impossible to arrange a satisfactory timing for the air transfer from the'pump cylinder H to the scavenge air belt F and thus into the cylinder B,

and would involve difliculties in connection with the scavenge cycle. Such a timing valve is preferably arranged as follows.

Above the pump cylinder H is a casing P which :extends horizontally and contains a ported liner Q and within this the rotary timingvalve R. The valve casing P'like the transfer passage G is preferably'formed integral with the crankcase J.

In the valve casing P is the main air inlet P controlled by the valve R with the passage which leads to the port or ports H through. which air is drawn into the cylinder H. The rotary valve R is driven in some convenient manner from the crankshaft K for example by means of a link extending between an eccentric on the crankshaft and a crankpin on the end of the valve. One embodiment of this feature is illustrated in Figures 2 and 3 of the drawings and will be later described. The valve R controls not only the air drawn through the passages P and port H into the cylinder H, but also the delivery of this air after compression from the port H into the transfer passage G. This delivery of the air charge'compressed in the displacer cylinder H takes place slightly before the commencement of the scavenging period. T'Ee value R cuts oil the displacer cylinder H and closes that end of the transfer passage after the scavenging ports B have been closed by the working piston 0.

Owing to the phasing'relation between the movements of the working piston O andof the piston J of the displacer pump and the timing effected bythe valve R, there is trapped in the scavenging belt F and in that portion of the transfer passage G which lies between the valve R and the scavenging belt F, air under a pressure substantially above the mean pressure existent throughout the scavenging period.

By the combination and arrangement of parts. .describedit is possible to obtain a good compromise with regard both to the balance and functioning of the engine.

The'arrangement by means of which the rotary yalve R is driven will be seen by reference to Figures 2 and 3. The valve R is mounted on a shaft R so as to be rotatable therewith. On one end of this shaft R is a crank pin R which is engaged by one arm 8 of a cross-shaped link driven by an eccentric K on the engine crankshaft K. This link has an arm S extending laterally and oppositely to the arm S and serving to drive a dynamo and other auxiliaries as may be seen in Figure 3. An upwardly directed arm S of the link engages a crank pin on the end of the valve-operating camshaft. A downwardly directed arm S drives an oil pump situated in the sump of the engine. The crank pin R of the shaft R which carries the rotary valve R also serves to drive through a drag link a water-circulating pump T.

With regard to the operation of the rotary valve R, this cooperates with ports Q and Q in theliner Q, these ports communicating respectively with the pump cylinder port H and the transfer passage G, while another part, not to be seen in Figure 1, communicates with the main air inlet P In the valve R the part R seen in Figure 2 controls the delivery of air from the pump into the transfer passage. The parts R control the suction through the inlet pipe P to the pump. 1 p I What I claim as my invention and desire to secure by Letters Patent is:

1. In an internal combustion engine operating on the two-stroke cycle the combination of 9. cylinder, a piston therein acting on a crankshaft through a connecting rod. ports in the cylinder wall uncovered by the piston towards the end of its outstroke, through which ports scavenge air flows from ascavenge air belt around these ports, a pump comprising a cylinder and piston reciprocating therein, a guide rod extending through the piston and throughout the length of the cylinder on which rod the piston reciprocates, the ends of this guide rod being rigidly carried by the ends of the cylinder, a transfer passage extending between the end of the pump cylinder and the said scavenge air belt, a valve located in through a connecting rod, ports in the cylinder ciprocating therein, the pump cylinder beingmounted with its axis at right angles to and below the level of the crankshaft axis and approximately at right angles to the axis of the working cylinder, a guide rod extending through the. piston and throughout the length of the cylinderon which rod thepiston reciprocates, the ends of this guide rod being rigidly carried by the ends of the cylinder, 9. transfer passage extending between the end of the pump cylinder and the said scavenge air belt, a valve located in the transfer passage adjacent to the pump, and a link connecting the pump piston to .the connecting rod of the working piston for driving the pump from and at the same speed as the crankshaft but out of phase with the working piston.

HARRY RALPH RICARDO. 

